The purpose of the present investigation is to study the effect of 3-methylcholanthrene induction on the metabolism of (-)r-7,t-8-dihydroxy-7,8-dihydrobenzo(a)pyrene, by high pressure liquid chromatography, in liver and lung microsomes of C57BL/6N and DBA/2N mice that are "responsive" and "non responsive" to polycyclic aromatic hydrocarbon induction of aryl hydrocarbon hydroxylase.